New research suggests that the heart slows down with age because of a group of cells in the
right atrium that acts as an internal pacemaker.

Researchers from the University of Colorado School of Medicine recorded spontaneous electrical
signals from those cells in old mice and found that they simply could not keep up with those from
younger mice.

The findings, which were published last week in
Proceedings of the National Academy of Sciences, suggest a possible treatment for heart
fatigue in older people.

“We know that you can stimulate these cells, so if you could provoke them just a little bit
more, you could boost the maximum heart rate just a little,” said physiologist Catherine Proenza,
an author of the study.

Answer to the old teeth-and-scales question

Scientists have long wondered which came first, teeth or scales. A new analysis of some
toothlike fossils suggests the answer might be scales.

The idea that teeth came first was based largely on 500 million-year-old fossil fragments, known
as conodonts, that look like teeth or spines and contain tissue that resembles dentin and
enamel.

Now, using high-resolution X-rays to study conodonts from several centuries, a team of
paleontologists has determined that they are not directly related to vertebrate teeth.

“If you look at ancestors of conodonts, what you see is gradual assembly of toothlike
characteristics” rather than a direct evolutionary progression, said an author of the study, Philip
C.J. Donoghue, a paleobiologist at the University of Bristol in England.

The researchers, who published their findings in
Nature, also reported that the conodonts did not contain dentin, “so the whole hypothesis
collapses,” Donoghue said.